Then you'd have to show that hatred towards trans people was likely as a result of the words
My understanding is that, in England at least, a hate crime depends on how it is perceived by the "victim", not the person committing the crime. Which makes this:
"criminalises spoken and written words likely to “stir up hatred”, even unintentionally, towards people based on certain characteristics"
Very problematic. As I read it JKRs post alone would be considered hate speech by TRAs, which means that is how it would be treated. In addition her post garnered thousands of likes and retweets and inspired probably hundreds of spin off posts, media articles etc. Definitely stirring up...
This potential law is terrifying and incredibly poorly thought through. (I also strongly suspect it won't include sex as a characteristic)